Something miraculous happened during the 20th century that rarely gets mentioned along with techno-leaps like the airplane, television, radio, A-bomb and the internet: due to improved public health, medicine and nutrition the average human lifespan on Earth doubled. The big question now is whether it could double again. Is there is a natural biological limit on human longevity, an age we just can’t get past? Or, given the right circumstances, could a lucky human give Methuselah a run for his money? Ben Guarino at The Washington Post reports that a new study of very old Italians suggests that there isn’t a cap on how long a human can keep going in this mortal coil.
The science of longevity is surprisingly controversial, mainly because there are so few people of extreme old age—defined at 110 years or older—around to study. So researchers look to statistics to try and figure out how long people can live. Guarino reports that in 1825, actuary Benjamin Gompertz put forth the idea that the odds of dying grow exponentially as we age. Further research bears that out. Between the age of 30 and 80, the odds of dying double every 8 years. What happens after that, however, is not completely figured out.
According to a controversial study released in 2016, which analyzed data from 40 different countries, the average person could make it to 115 with the right genes and interventions, and a few genetic superstars would be able to make it to 125. But that was it, they argued. There was a wall of mortality that medicine and positive thinking simply cannot overcome.
But not everyone is convinced by that data. That’s why for the new paper in the journal Science, researchers looked at the lifespans of 3,836 people in Italy who reached the age of 105 or older between 2009 and 2015, with their ages verified by birth certificates. What they found is that the Gompertz law goes a little haywire around the century mark. According to a press release, a 90 year old woman has a 15 percent chance of dying in the next year, and an estimated six years left to live. At age 95, the chance of dying per year jumps to 24 percent. At the age of 105, the chance of dying makes another leap to 50 percent. But then, surprisingly, it levels off, even past 110. In other words, at least statistically, each year some lucky person could flip the coin of life, and if it comes up heads every time, they could live beyond 115 or 125.
“Our data tell us that there is no fixed limit to the human lifespan yet in sight,” senior author Kenneth Wachter of UC Berkeley says in the release. “Not only do we see mortality rates that stop getting worse with age, we see them getting slightly better over time.”
Guarino reports that, while this study does not cover as many nations and data points as previous studies, the quality of data is much better. That’s because Italy keeps a pretty close watch on citizens, requiring them to register with their town of residence each year. That means researchers could confirm exactly when supercentenarians were born and died. Other nations, including the U.S.'s Social Security records, are not as accurate, and in many cases very old people tend to forget their exact age or add a couple years for prestige, which can pollute the data. “We have the advantage of better data,” Wachter tells Elie Dolgin at Nature. “If we can get data of this quality for other countries, I expect we’re going to see much the same pattern.”
So why would mortality rates level off at such an extreme age? Geneticist Siegfried Hekimi at McGill University in Montreal tells Carl Zimmer at The New York Times that cells in the body accrue damage, which is only partially repaired. (Hekimi was not affiliated with the study.) Over time, all that damage leads to aging of bodily systems and death. It’s possible that these extremely old people age more slowly, and their bodies are able to keep up with the repairs.
Jay Olshansky, a bio-demographer at the University of Illinois at Chicago, however, tells Dolgin that an endless plateau doesn’t make sense. Certain cells in the body like neurons, he says, do not replicate. Instead, they simply wither and die, placing a limit on how long humans can live.
So what can you do to stay alive until 115 or older? Guarino reports that lifestyle choices like eating right and exercise are great for expanding life expectancy in the first 70 or 80 decades of life. After that, though, it’s all up to genetics, and lifestyle doesn't seem to matter. One 104-year-old woman attributes her longevity to drinking 3 Dr. Pepper sodas per day for 40 years. The oldest man in the United States is 112 and smokes 12 cigars a day. And the world’s oldest verified woman, Jeanne Louise Calment who lived for 122 years and 164 days in France, smoked two cigarettes per day until age 119, only stopping because she could not see well enough to light up anymore.